Relationships were examined between the following variables: respiratory phase (R.P.) and intrathoracic pressure (I.T.P.); exercise intensity and I.T.P.; and whole body reaction movement and I.T.P., R.P. Intraesophageal balloon method was used to record the changes of I.T.P. The subjects were six young male volunteers. The following observations were made: 1)In accordance with the type of body movement, not only the positive but also the negative pressure changes were observed during dynamic body movements (situps, trunk extension, throwing, jumping and pressing). 2)A positive correlation was found between the exercise intensity and the amplitude of I.T.P. change. 3)Under the condition of unintentional respiration, breathholding after inspiration was the common phase of respiration at the commencement of a dynamic movement. 4)For the condition of waiting for signal, the shorter reaction time and movement time in whole body reaction movement were recorded in inspiratory breathholding state than in expiratory breathholding state. 5)During the whole body reaction movement commenced by the waiting condition of inspiratory breathholding, the changes of I.T.P. showed high amplitude in positive direction. When the signal was waited in expiratory breathholding state, I.T.P. change in negative direction preceded immediately before the pressure Change in positive direction. 6)These results suggested that the sharp positive change in I.T.P. is an essential factor for the commencement of an explosive movement mobilizing the large muscles of the body.

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